1. Field of the Invention
The invention relates generally to monitoring downhole equipment, and more specifically to systems and methods for installing optical fibers in downhole equipment without the need for splicing the optical fibers between different sections of the equipment.
2. Related Art
Oil production often requires the use of artificial lift systems to recover oil and other well fluids from wells. These artificial lift systems may include, for example, electric submersible pump (ESP) systems and subsea boosting systems. These systems are typically very expensive to install and operate. A subsea lift system may, for example, cost tens of millions of dollars to install and hundreds of thousands of dollars each day to operate. The costs associated with failures and downtime in these systems are also very high.
Because of the high cost of an artificial lift system such as may be installed in subsea applications, it is very important to take steps to ensure that it is as reliable as possible and has the longest possible operational life. One of the things that can be done to improve reliability is to monitor various parameters associated with the system in order to determine the “health” of the system. These parameters may include such things as temperature, pressure, vibration, fluid flow, fluid viscosity, voltage, current, and many others.
If the monitored parameters remain within desired operating ranges (a “green” zone), the system may continue to operate without any changes. If the monitored parameters fall outside the desired operating ranges, but are still within acceptable limits (a “yellow” zone), it may be necessary to adjust the operation of the system in some manner. This may include modifying control signals, updating operating parameters within the downhole equipment, and so on. These adjustments are intended to move the operation of the system (as indicated by the monitored parameters) back into the green operating zone. If the adjustments do not cause the parameters to return to the desired operating ranges, this may indicate that it is necessary to perform repair or maintenance on the system. If the monitored parameters fall outside the range of acceptable values (a “red” zone), it may be necessary to discontinue operation of the system, and possibly repair or replace one or more system components.
One of the key parameters that may be monitored is the temperature of the system components that are positioned downhole within a well. In some applications, the temperature can be as high as 600° F. High temperatures can be very hard on components such as motor bearings, and even materials such as electrical insulation, which may begin to break down and lose its electrically insulating properties. Conventionally, thermal sensors such as thermocouples were designed into equipment such as ESP motors to provide information on the temperature of the equipment. A thermocouple, however, can only monitor the temperature at a single point, so multiple thermocouples would be required to provide temperature information from different points within the equipment.
More recently, optical fibers that incorporate multiple sensors (fiber Bragg gratings) have been incorporated into the designs of equipment such as ESP motors in order to provide temperature information from multiple points within the motors. These types of sensors also have some drawbacks, however. For instance, in some applications, it may be necessary for an ESP motor to be several hundred feet long in order to generate the required horsepower to drive the associated pump. Because it would be very difficult to transport a motor of this size from the factory to the field where it will be installed, it is typically necessary to construct the motor in sections, each of which is less than 40 feet in length. If fiber optic sensors are incorporated into the motor sections, means must be provided to splice together the optical fibers of adjacent motor sections in the field when the motor is assembled and installed in the well. Currently available means to achieve the splices are expensive, slow and difficult to assemble, and too large to be accommodated in downhole motors.
It would therefore be desirable to provide means to facilitate the use of fiber optics in downhole equipment such as multi-section ESP motors which reduce or overcome one or more of the problems above.